The Effect of Planetary Flybys on Singly Synchronous Binary Asteroids

Binary asteroids form a significant portion of near-Earth asteroids, comprising at least 15% of the population. The method of formation for these systems is understood to be caused by YORP spin-up and fission, which can eventually lead the system into a stable state with the secondary rotating synchronously and in a near circular orbit. While many binary asteroids have been seen to lie in such a state, there are a significant number that exist at different levels of excitation for unclear reasons. Specifically, some binary secondaries are seen to be asynchronous and can exhibit chaotic orbital and rotational behavior. We investigate the role planetary flybys have on the excitation of binary asteroids, particularly the libration of the secondary. A major roadblock to accurately modeling binary asteroid evolution is accounting for the fully coupled rotational and translational motion of the binary components. The General Use Binary Asteroid Simulator code allows for relatively fast and accurate orbit propagation of this fully coupled two body problem (Davis and Scheeres, Icarus 2020). We have added the capability to the GUBAS code to track the effect a gravitational third body has on the binary asteroid, allowing for the modeling of either planetary flybys or solar perturbations. The model accurately accounts for the effect of the third body on the rotational and relative orbit of the binary components. Using this program, we have shown that a single distant planetary flyby can excite the binary asteroid secondary’s libration state. Using these results, this talk will investigate the effect various planetary encounters have on the mutual binary orbit and libration of the secondary. A series of Monte-Carlo simulations will provide a range of planetary flybys to perturb a stable, synchronous binary asteroid. The resulting motion will allow us to categorize how various encounters affect the motion and spin state of the secondary. Given past knowledge of a binary asteroid’s heliocentric orbit and planetary close approaches, the measurement of its current libration motion can be an important constraint on the rate of energy dissipation of the systems. This talk will present our current results in this topic.